Field of the Invention
The invention relates to a method and an apparatus for producing solid fertilizer from liquid substances such as manure from livestock or sludge.
Liquid manure production around the world is enormous. The escape of gases from liquid manure is not only malodorous but it also contributes to the global greenhouse effect and the much publicized ozone hole. Moreover, liquid manure is a danger to the groundwater when--in the old, time-honored way--the liquid manure, in its original form, is spread, as fertilizer on agricultural areas by spraying onto or other introduction into the soil. Similar problems are associated with the immense worldwide production of sludge, for instance from water purification systems.
There is accordingly a need for alternative methods that solve these problems associated with liquid manure and sludge in an environmentally appropriate manner and that at the same time enable the utilization, for soils used in agriculture, of the valuable substances contained in the fertilizer.
Two basic principles have been heretofore known in the art of processing liquid manure. In one of the two versions, the solids contained in the manure (amounting to approximately 3 to 8% by weight) are separated from the liquid phase, and the two phases are further processed separately from one another. The solid component contains the substances that are of high value as fertilizers; but more than 90% of the manure is liquid, and even after separation from the solid component it is "polluted" with residual compounds of dissolved substances (above all, nitrogen compounds). It is, accordingly, illegal for the liquid manure to be fed into surface waters such as brooks, rivers, lakes or ponds.
A system operating by the separation principle was put into operation in Fehring (in the Styria province of Austria) in 1990. There, the solids are separated out of the liquid manure and dried with the aid of methane produced in the anaerobic treatment of the liquid portion of the liquid manure. Additives are then blended with the dried solid, thus increasing the fertilizer value of the product. The liquid component of the manure is subjected to an anaerobic pretreatment and a chemical post-treatment, but until now it was never possible to achieve the degree of purity required by environmental laws. Feeding into surface waters, therefore, is illegal. Moreover, because of the expenditure for components and equipment for a liquid manure processing system employing the aforementioned principle, such high investment and operating costs are involved that the affected livestock keepers could hardly afford them without generous aid from governmental aid programs.
In the second principle for processing liquid manure, the manure is not separated into its solid component and its liquid phase. Instead, the manure is left in its original form and is blended with harvest waste. In the simplest possible form, in livestock keeping this is done on straw bedding in the animal stalls in the stable or barn; after some time, after lodging there and rotting with ensuing composting, the muck in the stalls turns into a fertilizer, of the kind that has for eons been spread on the fields to be fertilized. However, this does not solve the complicated environmental problem presented by liquid manure.
An improvement to the situation had been hoped for with the method described in a document entitled HUT04218. In it, agricultural waste is collected on stubble fields (or at other locations where it occurs) and stored, compacted into bales. When liquid manure is then to be prepared, the baled waste is supposed to be comminuted with a bale plucking machine and chopped up until pieces of straw or other waste that are less than approximately 25 mm in size are created, which can easily be blended with the liquid manure. According to that document, the resultant mixture should either be usable as fertilizer after composting or should be usable as fuel for heat production in automatically controlled boiler systems.
The mixture of harvest leftovers in liquid manure produced by the method described in that document is in fact handy and easy to manipulate, as this inventor has been able to confirm in series of tests for replicating and checking the efficiency of the method described. Nevertheless, the liquid manure is neither fully absorbed nor bound by the pieces of waste that are up to 25 mm in size, nor can any chemical reactions of the liquid manure with the waste be demonstrated; on the contrary, there is a heterogeneous mixture of waste in liquid manure, from which the unmodified liquid manure, whose consistency is unchanged, can drain out and seep into the soil beneath, which does not eliminate the threat to groundwater, nor is the malodorous escape of gases from the liquid manure prevented. Accordingly, the dangers to the atmosphere are not obviated and pollution is still rampant. Nor are these grave disadvantages even perceptibly --and certainly not completely--eliminated by composting the mixture as recommended.